Antibiotic Resistance Strategy And Environmental Adaptation Mechanism Of Acinetobacter Johnsonii

Studies have shown that Acinetobacter johnsonii is widely distributed in the natural environment and even in the clinical environment with high antibiotic selective pressure,and could cause some human diseases.Previous laboratory study showed that the distribution of A.johnsonii in the Ba River was affected by antibiotics and other pollutants.Besides,most bacteria have a biofilm lifestyle in natural environments.Except for the antibiotic resistance conferred by antibiotic resistance determinants,biofilms can also enhance the tolerance of bacteria under adverse conditions.However,whether A.johnsonii has such a resistance mechanism is currently unclear.In this study,the relationship among antibiotic resistance determinants with bacterial phenotype and isolated environment were firstly analyzed at the genomic level through whole genomic sequence of A.johnsonii strains,and then,the environmental adaptability of A.johnsonii strains were visualized utilizing pan-genomic analysis.Meanwhile,based on the analysis of the biofilm formation ability of A.johnsonii strains,the role of biofilm in bacterial resistance was explored,and the response mechanism of different forms of A.johnsonii to antibiotics was further explained through transcriptomic analysis.The main results derived from this study are as follows:1.Antibiotic residue accumulation resulted in the formation of drug-resistant phenotypes and a rise in the proportion of strains with a high multiple antibiotic resistance(MAR)index.Whole-genome sequencing revealed no link between genome resistance determinants and phenotype,and horizontal transfer components of the genome,such as genomic island and prophage,included a substantial number of virulence associated genes but essentially no drug resistance determinants.Increased antibiotic residue levels result in the enrichment of genes linked with survival in the genome.Furthermore,the inclusion of small plasmids may improve A.johnsonii’s adaptation to the environment.2.The pan-genomic analysis of 16 strains of A.johnsonii from hospitals and water environments revealed that the A.johnsonii had good adaptability to different environments,but the genes associated with the fundamental process were mostly conserved and would not change with the change of environment during the evolution process.Hospital-derived strains,on the other hand,gained more functional genes correlated with post-translational modifications,encoding-lactamase,and defensive mechanisms in order to adapt to human hosts and the intense selection pressure exerted by antimicrobial drugs.Furthermore,the genomes of the majority of hospital-derived strains contain a range of exogenously acquired pathogenicity and ARGs.3.The majority of A.johnsonii showed a strong biofilm-forming capacity,however there was no significant difference in biofilm-forming ability amongst phenotypes.Biofilm production increases A.johnsonii ’s resistance to antibiotics like tetracycline,which limits biofilm formation by decreasing plankton growth.In addition,the proportion of persister bacteria was unaffected by strain phenotype.There was a greater proportion of persister bacteria in the biofilm compared to planktonic bacteria.4.Transcriptome analysis revealed that after biofilm formation,the expression levels of genes involved in oxidative phosphorylation and the citrate cycle were significantly down-regulated,while the expression levels of genes involved in sulfur metabolism were significantly up-regulated.The expression of ribosomal subunit-related genes was also significantly down-regulated,which resulted in a slower metabolism.Furthermore,due to the changes in the way of metabolism,the expression levels of genes related to specific amino acids and sulfide transport in the bacterial membrane were significantly up-regulated,and the expression levels of genes related to molybdate and phosphate transport were significantly down-regulated.The expression levels of genes related to tyrosine synthesis and metabolism pathways in planktonic bacteria were significantly up-regulated after treatment with sub-lethal concentration of tetracycline,and the expression level of Sec B gene was significantly up-regulated,while other genes involved in protein export pathway were significantly down-regulated.Sec B gene may facilitate the overexpression of the Sec B-Hic AB network to improve A.johnsonii viability under adverse circumstances.Mdf A,a multidrug-resistance efflux pump conferring to tetracycline resistance,was also overexpressed.However,only a few numbers of type IV pili and genes encoding extracellular polymeric substances(EPS)in the biofilm were significantly up-regulated after biofilm bacteria treatment with sub-lethal concentration of tetracycline.In summary,our work used genomic and transcriptomic methodologies to demonstrate A.johnsonii’s drug resistance strategy and the environmental adaptation characteristics of the genome from different levels,and establishes a theoretical foundation for further research into the distribution features and drug resistance tactics of bacteria in the natural environment.